TPS61022: enable pin

Hi Amr,

TPS61022 requires a 1.2V for enable pin. May I know your application's detailed information, such as input source voltage range, output voltage, output current range? 

I'll see if there is a suitable device or a solution.

Hi Zack,

thank you very much for your reply.

I have checked the datasheet and found the VEN_H of 1.2V and VEN_L of max 0.45V- If I rightly understood, the 1.2V is required only at Startup then if the voltage applied at the enable pin is reduced less than 1.2V, the device keeps powered till the enable pin voltage reaches 0.45V (hysteresis). Could you please confirm/ decline that?

there is another concern:

the load I currently connect to the TPS61022 is in most of the cases 50mA or less. At sometimes it increases to about 150mA. In this case, using the webbench, is it advises to set the load current at 150mA and assume 50mA is a light loading condition? Or is it much better to design at the 50mA and assume 150mA a relatively overload condition (still however 150mA very much less than the device rating)? Or to design at some current in between?

Kind Regards,

Amr

Hi Amr,

Actually there is no word of hysteresis for the enable pin voltage threshold in TPS61022 datasheet. The VEN_H of 1.2V and VEN_L of 0.45V is a logic level requirement. The enable pin voltage must be higher than 1.2V to enable to device and must be lower than 0.45V to disable to device. A voltage between 0.45V and 1.2V is not promised. 

Is the input a supercap? What's the output voltage? If your application is a backup power supply, you could connect ENABLE pin to Vout through a pull up resistor.

TPS61023 is more suitable for your application because the 8A boost converter TPS61022 is overkill for your application.

Hello Zack,

Thank you for the explanations and the suggestions.

The application is similar to TIDA01385 but the model of TPS61021A didn't function/required an extremely long simulation time  in TINA simulator that's why for checking of the idea of the whole system (by me the system is somehow modified other than TIDA01385), I temporarily moved to TPS61022 because it has an unencypted model that can be used with TINA simulator and it also requires relatively shorter time in the simulation.

You are right that the TPS61022 is very highly rated than the required specs in my application, and as you recommended, TPS61023 could be much better.

- With regard to overkilling of the application using the TPS61022, is it due to the very low efficiency at this very light loading condition? 

- Unfortunately I was unable to find a model for TPS61023 that is compatible with TINA simulator. May I ask you please if there is some model of TPS61023 that can be used with TINA simulator?

- the EN pin is currently directly connected to Vin. May you please attach some figure to show to pull up to Vout (currently set at 3.3V) while connected to Vin? May be one have to add some resistance between EN and Vin also.

you are right that the word "hysteresis" is not mentioned in the datasheet. And I was questioning if VH and VL are designed as hysteresis. It is now clear.

Regards,

Amr

Hello Zack,

thank you very much for the info. It works.

However, I noticed that also without adding the diodes that the input voltage at start should be higher than the EN voltage. But during normal operation, if Vin gets lower, it can still get as low as about 0.5 volt before the boost is disabled.

Below are the waveforms;

Vcap is the supercap voltage and Voboost is the output of the boost (set at 3.3V however).

May you please check that. Either the simulation model needs some modifications to cope with the actual performance or the actual performance has some hysteresis.

Kind Regards,

Amr

Hi Amr,

That's the feature of TPS61022 and TPS61023. 

The rising UVLO is 1.8V and falling UVLO is 0.5V. That means TPS61022 needs to start up from 1.8V supercap voltage at least. It is able to regulate the output voltage until supercap discharges to 0.5V. 

Hi Zack,

If I rightly understood, the UVLO assumes that the EN is still set at the 1.2V (through an external supply or whatever). But in the circuit we discuss, the VIN and EN pins are tied together, therefore both Vin and EN reach the 0.5V at the same time. Therefore, I was thinking why the IC isn't shutdown when the EN pin gets less than its 1.2V?

Regards,

Amr

Hi Amr,

The EN logic low spec in EC table is 0.35V minimum. The EN logic high spec in EC table is 1.2V maximum. These two value are the key spec in applications. It means if customer would like to enable the device completely, the EN voltage should be higher 1.2V. If customer would like to disable the device completely, the EN voltage should be lower than 0.35V. In another word, if the EN voltage is between these two spec, for example 0.8V, the device is either in active status and shutdown status. 

That's why in simulation, even the EN pin gets less than 1.2V, the device isn't shutdown.

Hi Zack,

Thanks alot. May be the official name of that isn't hysteresis. But from the simulations it looks exactly like hysteresis. At Startup Vin is less than than the 0.35V and the system is off. Vin still increases getting between the 0.35(0.45V) and the 1.2V but still system off till Vin reaches the 1.2V then the system is enabled. Now if Vin (tied to EN) gets less and going below the 1.2V the system still on till Vin reaches the 0.35-0.45V then the system is off. Isn't this hysteresis? May be there is no need for the diode connection in the previous message?

Regards,

Amr

Thanks Zack

Hello Zack,

Thank you very much for the info.

Kind Regards,

Amr